Incident at Chalfont & Latimer (21/06/20)

Metroman62

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The BBC London Transport correspondents is reporting a Chiltern service took a wrong signal at Chalfont and Latimer on the Metropolitan line and came very close to a Met line train.

This seems rather worrying.

https://twitter.com/BBCTomEdwards/status/1275110168104239110
@BBCTomEdwards: NEW: Photo shows how close the 2 trains on the Met line were to a collision. @chilternrailway train went the wrong way up the line damaging points and track. @raibgovuk investigating.
 
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goldenarrow

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Unsurprisingly there's tons of speculation without cigar on there. Even Mr Edwards source has got it slightly wrong, those actually in the know are quite rightly staying quiet on public domains for the time being. The last thing investigators need right now is a hounding from the press.
 

Townsend Hook

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The BBC London Transport correspondents is reporting a Chiltern service took a wrong signal at Chalfont and Latimer on the Metropolitan line and came very close to a Met line train.

My understanding of it is that the Chiltern train passed a red signal on approach to Chalfont and ran through a couple of sets of switches which were set for the Chesham service. Not speculating as to the cause, that’s up to the investigators.
 

SlimJim1694

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I saw some pictures of it on social media. I won't post them up here but they aren't hard to find. The Chiltern train only stopped about a coach length away from the tube train. I really hope there is another explanation (wrong side failure?) but I have to say it does look like a SPAD reset and continue at first glance.
 

Tetchytyke

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Not great timing as Chiltern have just applied to the ORR for a derogation from ATP rules in the case of equipment failure.
 

lonogrol

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The Chiltern train did not take a wrong signal, the signal was passed at danger.
As I understand it, the train was tripped correctly and all signaling equipment was working correctly.

There was a Metropolitan train in the N.B platform with a clear signal with the arbour lights indicating a route toward Chesham. the train operator noticed the signal went back on him so the train didn’t proceed very far at all. At the same time the Chiltern train had ran through one set of points that were set against him & then travelled over the crossover that was set to bring the Met train across.

It is quite a long way from the signal protecting this move, to where the train eventually stopped. On L.U.L trains, for a few minutes after being tripped, trains are subject to move at a restricted speed, to help
prevent or at least mitigate against incidences such as this. I have been told that Chiltern trains do not have this feature, which has a rather rude acronym.

the Chesham branch will be closed until Wednesday morning, as repairs are required to the points. Engineering hours in this area are quite short and there would be insufficient time to do the repairs tonight.
 

800002

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Is there not trip-cock protection in use on the Met line signals?
Edit: post above clarifies my question, many thanks.

None-the-less, and not withstanding the above comments, very scary indeed.

I will remain on the look out for official information that comes via the RAIB.
Quite a serious incident indeed unfortunately.
 
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I have no idea what happened here but several worrying things about this:
A: I wonder what speed the crossover was taken in order for the 165 to come to a rest so close to the S8
B: was the move signalled
C: why were the points set to cross the 165 from the down to the up with another train occupying the platform.

Obviously goes without saying but i hope both drivers are okay after such an incident. I know crash standards have improved but i dont think underground trains deal well being shunted by mainline ones...
 

traingeek97

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Did the 165 run into the Chesham bay platform?

Wouldn't like to say for sure but it looks like the London-bound 165 ran through the signal protecting Chalfont & Latimer junction, while a Northbound Metropolitan Line train was already routed across the junction to Chesham.
 
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Wouldn't like to say for sure but it looks like the London-bound 165 ran through the signal protecting Chalfont & Latimer junction, while a Northbound Metropolitan Line train was already routed across the junction to Chesham.

That is the assumption i made as a s8 cant fit in the bay platform, and therefore the only reasonable assumption
 

SlimJim1694

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It is quite a long way from the signal protecting this move, to where the train eventually stopped. On L.U.L trains, for a few minutes after being tripped, trains are subject to move at a restricted speed, to help
prevent or at least mitigate against incidences such as this. I have been told that Chiltern trains do not have this feature, which has a rather rude acronym.
I dont know about the Underground tripcock system, but with nornal TPWS there is a 60 second brake release time out built in to the reset button (at least on the units I drive) so you've got a bit of thinking time at least to wonder why you came up I a heap and hopefully do the right thing. Do Chiltern units have this 60 second timeout when tripped in the Underground section or can they just carry on as normal?

I was looking at jobs with Chiltern and hadn't factored in all the Underground extra rules they do.
 

PeterC

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Did the 165 run into the Chesham bay platform?
That would be an achievement as, IIRC, the bay can only be accessed from the branch.

The Met Line Twitter feed first called it a "signal failure" and then changed to "emergency engineering" with no hint as to seriousness.
 

PeterC

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I have no idea what happened here but several worrying things about this:
A: I wonder what speed the crossover was taken in order for the 165 to come to a rest so close to the S8
B: was the move signalled
C: why were the points set to cross the 165 from the down to the up with another train occupying the platform.

Obviously goes without saying but i hope both drivers are okay after such an incident. I know crash standards have improved but i dont think underground trains deal well being shunted by mainline ones...
I have no knowledge of the situation but looking at the photo and from my knowledge of the junction as a passenger:
B: SPAD?
C: I would assume that the points were set to cross a northbound Chesham from platform 3 to the branch. In such a situation a southbound 165 could go through the trailing points for the branch and follow the crossover in the opposite direction.
 

MarkyT

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Not great timing as Chiltern have just applied to the ORR for a derogation from ATP rules in the case of equipment failure.
I don't think that's relevant here as it is LU infrastructure and all trains use the mechanical trainstop system. The cl.165s that work the service are specially fitted with trip cocks for this. The up home signal is about 700m clear of the junction, which is likely to be a full emergency braking distance overlap at the line speed, as per usual LU signalling practice.
 

theageofthetra

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Just to clarify, at this location is TPWS fitted, or is this entirely LU infrastructure with their own protection systems?
 

bramling

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Just to clarify, at this location is TPWS fitted, or is this entirely LU infrastructure with their own protection systems?

LU. No TPWS, but the standard LU trainstop/tripcock system. Must admit I’m surprised the Chiltern trains don’t have the speed control after tripping system, this never crossed my mind before as I just assumed they had it.

It is no exaggeration to say this could have been a collision - whatever the cause this is clearly an extremely serious near-miss, as had the LU train departed on a green before the Chiltern train returned or maintained the signal at danger then there would have been nothing further apart from the drivers eyes (or perhaps if the signaller noticed and was able to do a radio call in time) to separate both trains.

Something not massively dissimilar occurred at Edgware a decade or so ago, in that case a SPAD followed by reset and continue. In that incident again occupation of track circuits fortunately maintained a signal at danger that being approach-cleared had fortunately not yet cleared for its rightful movement.
 

MarkyT

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Just to clarify, at this location is TPWS fitted, or is this entirely LU infrastructure with their own protection systems?
This is LU infrastructure and thus has their signalling and train protection provided by mechanical train stops as far as I know unless things have changed recently under the 4 lines modernisation project. I don't think the work has got that far along the Metropolitan though and the clearly visible red signal in the BBC tweet suggests the signalling is still traditional. The class 165s that work this route are specially fitted with trip cocks.
 

rebmcr

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If I'm correctly understanding the posts about signal distance, and cooldowns after a trainstop activation, it seems evident that the 165 was supposed to stop before the points being protected by the Danger signal, and possibly ended up traversing them because of an unconfirmed reset-and-continue?
That would seem to make sense as a design that would protect the side of S8s during their conflicting move onto the Chesham track.
 

bramling

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If I'm correctly understanding the posts about signal distance, and cooldowns after a trainstop activation, it seems evident that the 165 was supposed to stop before the points being protected by the Danger signal, and possibly ended up traversing them because of an unconfirmed reset-and-continue?
That would seem to make sense as a design that would protect the side of S8s during their conflicting move onto the Chesham track.

Essentially yes. My understanding is the Chiltern train should have been brought to a stand at the southbound home signal. In advance of this signal would be a calculated full-speed braking distance overlap, followed by three sets of points, all of which were set reverse to allow the LU train to access the Chesham branch (in fact there’s a further two sets of rarely-traversed points there, which weren’t directly involved). The Chiltern train ran through the first set of points which were set against it, then followed the second and third sets of points which were reversed for the LU train’s move onto the Chesham branch. This took it from the southbound to northbound roads and now directly head-on towards the LU train.

So there could have been a side-swipe between the two trains or even a full head-on collision depending on whether the LU train had moved off, as it had been apparently signalled to do.

I’m not going to speculate further as to how the Chiltern train might have got as far as breaching the overlap of the home signal. In very general terms there’s a number of ways this could potentially happen.
 
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Townsend Hook

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This is LU infrastructure and thus has their signalling and train protection provided by mechanical train stops as far as I know unless things have changed recently under the 4 lines modernisation project. I don't think the work has got that far along the Metropolitan though and the clearly visible red signal in the BBC tweet suggests the signalling is still traditional. The class 165s that work this route are specially fitted with trip cocks.

The 4LM plan is currently suspended due to the financial pressure TfL are under due to COVID-19, and in any case was never planned to cover lines shared with Chiltern, so that Chiltern units don’t have to be fitted with CBTC.
 

bramling

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I have no idea what happened here but several worrying things about this:
A: I wonder what speed the crossover was taken in order for the 165 to come to a rest so close to the S8
B: was the move signalled
C: why were the points set to cross the 165 from the down to the up with another train occupying the platform.

Obviously goes without saying but i hope both drivers are okay after such an incident. I know crash standards have improved but i dont think underground trains deal well being shunted by mainline ones...

Something like an S stock I suspect wouldn’t fare too badly against a 165, being of a not dissimilar construction and essentially the same size.

The Bakerloo north of Queen’s Park is perhaps more of an issue. A 378 versus a 72 Tube stock certainly wouldn’t be a fair contest even at comparatively low speed. Indeed a 59 stock car was virtually demolished when it was rear-ended by a 313 near Kensal Green in the 1980s.
 

Mojo

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The 4LM plan is currently suspended due to the financial pressure TfL are under due to COVID-19, and in any case was never planned to cover lines shared with Chiltern, so that Chiltern units don’t have to be fitted with CBTC.
That isn’t quite true, the programme as originally designed (and is still the official plan) would involve the new signalling covering the entirety of the sub surface network, but with the new signalling overlayed or underlayed depending on the location to still enable lineside signals to work for trains that will not have the technology. Of course that is off topic for this thread so shan’t go into more detail but please start a new thread if you are interested.
 

lonogrol

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I dont know about the Underground tripcock system, but with nornal TPWS there is a 60 second brake release time out built in to the reset button (at least on the units I drive) so you've got a bit of thinking time at least to wonder why you came up I a heap and hopefully do the right thing. Do Chiltern units have this 60 second timeout when tripped in the Underground section or can they just carry on as normal?
I don’t know, just that their trains after resetting do not have S.C.A.T,
so accordingly immediately after resetting, it is possible to wind up and resume full speed.
A: I wonder what speed the crossover was taken in order for the 165 to come to a rest so close to the S8
B: was the move signalled
C: why were the points set to cross the 165 from the down to the up with another train occupying the platform.
A- the crossover is pretty much off the end of the platform, although is over a kilometre from the signal the train should have stopped at
B- this is not a signaled move. There is only one route from the signal the Chiltern train passed at danger, and that is straight into the S.B platform
C- the points were set to carry the Met train across to the S.B line, then a short while along is another set of points to go over to the Chesham branch, you can see this on the Carto metro map. They were not set for the 165.
 

Nicholas43

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Is it surprising, or what's designed to happen, that the Chiltern train bounced over the first set of points and continued along the track?
 

matt_world2004

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The 4LM plan is currently suspended due to the financial pressure TfL are under due to COVID-19, and in any case was never planned to cover lines shared with Chiltern, so that Chiltern units don’t have to be fitted with CBTC.
I thought they covered lines shared with Chiltern with a red , green and white signalling system with white being proceed in ATO mode only
 

Mojo

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Is it surprising, or what's designed to happen, that the Chiltern train bounced over the first set of points and continued along the track?
Continued along the track as opposed to what?
 

SlimJim1694

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Is it surprising, or what's designed to happen, that the Chiltern train bounced over the first set of points and continued along the track?

To understand what happened you need to understand the difference between trailing and facing points. The first set of points the Chiltern train encountered were trailing and set against the Chiltern train so it ran through them. A train doesn't bounce over incorrectly set trailing points, it forces it's way THROUGH them. The second set were facing to it, which is why it crossed to the opposite line directly facing the underground train that had the road.
 

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